<template>
    <div class="pagination">
      <button :disabled="pageNo==1" @click="$emit('getPageNo',pageNo-1)">上一页</button>
      <button v-if="startNumAndEndNum.start > 1" @click="$emit('getPageNo',1)" :class="{active:pageNo==1}">1</button>    
      <button v-if="startNumAndEndNum.start > 2">•••</button>

        <!-- 中间部分 -->
      <button v-for="(page,index) in startNumAndEndNum.end" :key="index" v-if="page >= startNumAndEndNum.start" @click="$emit('getPageNo',page)" :class="{active:pageNo==page}">{{ page }}</button>

      <button v-if="startNumAndEndNum.end < totalPage - 1">•••</button>
      <button v-if="startNumAndEndNum.end < totalPage" @click="$emit('getPageNo',totalPage)" :class="{active:pageNo==totalPage}">{{totalPage}}</button>
      <button :disabled="pageNo==totalPage" @click="$emit('getPageNo',pageNo+1)">下一页</button>
      
      <button style="margin-left: 30px">共 {{total}} 条</button>
    </div>
</template>

<script>
export default {
    name: "Pagination",
    props:['pageNo','pageSize','total','continues'],
    computed:{
        //总共多少页
        totalPage(){
            //向上取整
            return Math.ceil(this.total/this.pageSize);
        },
        //计算出连续的页码的起始数字与结束数字
        startNumAndEndNum(){
            const {continues,pageNo,totalPage} = this;
            //先定义两个变量起始数字与结束数字
            let start = 0,
             end = 0;
            //连续页码数字5【就是至少5页】 如果出现不正常的现象【就是不够5页】
            //不正常现象【总页数没有连续页码数多】
            if(continues > totalPage){
                 start = 1;
                 end=totalPage;
            }else{
                //正常现象【连续页码5，但是总页数一定是大于5的】
                // 起始数字
                start = pageNo - parseInt(continues / 2);
                //结束数字
                end = pageNo + parseInt(continues / 2);          
       
                //把出现不正常的现象【start数字出现0|负数】纠正
                if(start < 1){
                    start = 1,
                    end = continues;
                }
                //把出现不正常的现象【end数字大于总页码数】纠正
                if(end > totalPage){
                    end = totalPage,
                    start = totalPage - continues + 1;
                }
            }
            return{start,end}
        }
    }
}
</script>

<style lang="less" scoped>
.pagination {
    text-align: center;
    button {
    margin: 0 5px;
    background-color: #f4f4f5;
    color: #606266;
    outline: none;
    border-radius: 2px;
    padding: 0 4px;
    vertical-align: top;
    display: inline-block;
    font-size: 13px;
    min-width: 35.5px;
    height: 28px;
    line-height: 28px;
    cursor: pointer;
    box-sizing: border-box;
    text-align: center;
    border: 0;

    &[disabled] {
        color: #c0c4cc;
        cursor: not-allowed;
    }

    &.active {
        cursor: not-allowed;
        background-color: #409eff;
        color: #fff;
    }
    }
}
.active{
    background: skyblue;
}
</style>
